- ID:
- ivo://CDS.VizieR/J/ApJ/758/129
- Title:
- 4Ms Chandra Deep Field South 6-8keV galaxies
- Short Name:
- J/ApJ/758/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the 4Ms Chandra Deep Field-South (CDF-S) survey, we have identified a sample of 6845 X-ray-undetected galaxies that dominates the unresolved {approx}20%-25% of the 6-8keV cosmic X-ray background (XRB). This sample was constructed by applying mass and color cuts to sources from a parent catalog based on GOODS-South Hubble Space Telescope z-band imaging of the central 6' radius area of the 4Ms CDF-S. The stacked 6-8keV detection is significant at the 3.9{sigma} level, but the stacked emission was not detected in the 4-6keV band, which indicates the existence of an underlying population of highly obscured active galactic nuclei (AGNs). Further examinations of these 6845 galaxies indicate that the galaxies on the top of the blue cloud and with redshifts of 1<~z<~3, magnitudes of 25<~z_850_<~28, and stellar masses of 2x10^8^<~M_{sstarf}_/M_{sun}_<~2x10^9^ make the majority contributions to the unresolved 6-8keV XRB. Such a population is seemingly surprising given that the majority of the X-ray-detected AGNs reside in massive (>~10^10^M_{sun}_) galaxies. We discuss constraints upon this underlying AGN population, supporting evidence for relatively low mass galaxies hosting highly obscured AGNs, and prospects for further boosting the stacked signal.
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- ID:
- ivo://CDS.VizieR/J/ApJ/831/145
- Title:
- 6Ms Chandra long-term analyses of AGNs
- Short Name:
- J/ApJ/831/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform long-term (~15 years, observed-frame) X-ray variability analyses of the 68 brightest radio-quiet active galactic nuclei (AGNs) in the 6Ms Chandra Deep Field-South survey; the majority are in the redshift range of 0.6-3.1, providing access to penetrating rest-frame X-rays up to ~10-30keV. Of the 68 sources, 24 are optical spectral type I AGNs, and the rest (44) are type II AGNs. The timescales probed in this work are among the longest for X-ray variability studies of distant AGNs. Photometric analyses reveal widespread photon flux variability: 90% of AGNs are variable above a 95% confidence level, including many X-ray obscured AGNs and several optically classified type II quasars. We characterize the intrinsic X-ray luminosity (L_X_) and absorption (N_H_) variability via spectral fitting. Most (74%) sources show L_X_ variability; the variability amplitudes are generally smaller for quasars. A Compton-thick candidate AGN shows variability of its high-energy X-ray flux, indicating the size of reflecting material to be <~0.3pc. L_X_ variability is also detected in a broad absorption line quasar. The N_H_ variability amplitude for our sample appears to rise as time separation increases. About 16% of sources show N_H_ variability. One source transitions from an X-ray unobscured to obscured state, while its optical classification remains type I; this behavior indicates the X-ray eclipsing material is not large enough to obscure the whole broad-line region.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A111
- Title:
- Multi-color detection of gravitational arcs
- Short Name:
- J/A+A/567/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Strong gravitational lensing provides fundamental insights into the understanding of the dark matter distribution in massive galaxies, galaxy clusters and the background cosmology. Despite their importance, the number of gravitational arcs discovered so far is small. The urge for more complete, large samples and unbiased methods of selecting candidates is rising. A number of methods for the automatic detection of arcs have been proposed in the literature, but large amounts of spurious detections retrieved by these methods forces observers to visually inspect thousands of candidates per square degree in order to clean the samples. This approach is largely subjective and requires a huge amount of eye-ball checking, especially considering the actual and upcoming wide field surveys, which will cover thousands of square degrees. In this paper we study the statistical properties of colours of gravitational arcs detected in the 37deg^2^ of the CARS survey.
- ID:
- ivo://CDS.VizieR/J/AJ/122/1718
- Title:
- Multicolor photometry in Abell 2634
- Short Name:
- J/AJ/122/1718
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An optical photometric observation with the Beijing-Arizona-Taipei-Connecticut multicolor system is carried out for the central region of the nearby cluster of galaxies Abell 2634. From the 2Kx2K CCD images with 14 filters, which cover a range of wavelength from 3600 to 10000{AA}, 5572 sources are detected down to V~20mag in a field of 56'x56' centered on this regular cluster of galaxies. As a result, we achieved the spectral energy distributions (SEDs) of all sources detected. There are 178 previously known galaxies included in our observations, 147 of which have known radial velocities in the literature. After excluding the foreground and background galaxies, a sample of 124 known members is formed for an investigation of the SED properties. The comparison of observed SEDs of the early-type member galaxies with the template SEDs demonstrates the accuracy and reliability of our photometric measurements.
- ID:
- ivo://CDS.VizieR/J/ApJS/149/53
- Title:
- Multicolor photometry of A2255 galaxies
- Short Name:
- J/ApJS/149/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our optical multicolor photometry for the nearby cluster of galaxies A2255 with 13 intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system (see Cat. II/262), which cover an optical wavelength range from 3000 to 10000{AA}. The spectral energy distributions (SEDs) in the optical band for more than 7000 sources are achieved down to V~20 in a field of 58'x58' entered on this rich cluster. A2255 has been observed by the Sloan Digital Sky Survey (SDSS) down to V~17.5 spectroscopically and r'~22.0 photometrically. A method of combining the SDSS photometric data in five broad bands and the BATC SEDs is then explored. A sample of 254 galaxies with known redshifts in the region of A2255 is constructed for testing the reliability of the method of combining SEDs. Our application of the technique of photometric redshift on this sample shows that the combined SEDs with higher resolution could lead to a more accurate estimate of photometric redshift. Based on 214 spectroscopically confirmed member galaxies, spatial and dynamical properties of this cluster are studied.
- ID:
- ivo://CDS.VizieR/J/A+A/556/A55
- Title:
- Multi-color photometry of star-forming galaxies
- Short Name:
- J/A+A/556/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We estimate the galaxy stellar mass function and stellar mass density for star-forming and quiescent galaxies with 0.2<z<4. We construct a large, deep sample of galaxies selected using the new UltraVISTA DR1 data release (Cat. J/A+A/544/A156). Our analysis is based on precise 30-band photometric redshifts. By comparing these photometric redshifts with 10800 spectroscopic redshifts from the zCOSMOS bright (Cat. J/ApJS/172/70) and faint (Lilly et al. in prep) surveys, we find an accuracy of sigma(dz/(1+z))=0.008 at i<22.5 and sigma(dz/(1+z))=0.03 at 1.5<z<4.
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/3324
- Title:
- Multicomponent matched filter test
- Short Name:
- J/MNRAS/474/3324
- Date:
- 02 Mar 2022 00:06:44
- Publisher:
- CDS
- Description:
- We describe a multicomponent matched filter (MCMF) cluster confirmation tool designed for the study of large X-ray source catalogues produced by the upcoming X-ray all-sky survey mission eROSITA. We apply the method to confirm a sample of 88 clusters with redshifts 0.05<z<0.8 in the recently published 2RXS catalogue from the ROSAT All-Sky Survey (RASS) over the 208 deg^2^ region overlapped by the Dark Energy Survey (DES) Science Verification (DES-SV) data set. In our pilot study, we examine all X-ray sources, regardless of their extent. Our method employs a multicolour red sequence (RS) algorithm that incorporates the X-ray count rate and peak position in determining the region of interest for follow-up and extracts the positionally and colour-weighted optical richness {lambda}_MCMF_ as a function of redshift for each source. Peaks in the {lambda}_MCMF_-redshift distribution are identified and used to extract photometric redshifts, richness and uncertainties. The significances of all optical counterparts are characterized using the distribution of richnesses defined along random lines of sight. These significances are used to extract cluster catalogues and to estimate the contamination by random superpositions of unassociated optical systems. The delivered photometric redshift accuracy is {delta}z/(1+z)=0.010. We find a well-defined X-ray luminosity-{lambda}_MCMF_ relation with an intrinsic scatter of {delta}ln({lambda}_MCMF_|Lx)=0.21. Matching our catalogue with the DES-SV redMaPPer catalogue yields good agreement in redshift and richness estimates; comparing our catalogue with the South Pole Telescope (SPT) selected clusters shows no inconsistencies. SPT clusters in our data set are consistent with the high-mass extension of the RASS-based {lambda}_MCMF_-mass relation.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/68
- Title:
- Multi-epoch VLBA imaging of 20 Tev blazars
- Short Name:
- J/ApJ/853/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 88 multi-epoch Very Long Baseline Array (VLBA) images (most at an observing frequency of 8GHz) of 20TeV blazars, all of the high-frequency-peaked BL Lac (HBL) class, that have not been previously studied at multiple epochs on the parsec scale. From these 20 sources, we analyze the apparent speeds of 43 jet components that are all detected at four or more epochs. As has been found for other TeV HBLs, the apparent speeds of these components are relatively slow. About two-thirds of the components have an apparent speed that is consistent (within 2{sigma}) with no motion, and some of these components may be stationary patterns whose apparent speed does not relate to the underlying bulk flow speed. In addition, a superluminal tail to the apparent speed distribution of the TeV HBLs is detected for the first time, with eight components in seven sources having a 2{sigma} lower limit on the apparent speed exceeding 1c. We combine the data from these 20 sources with an additional 18 sources from the literature to analyze the complete apparent speed distribution of all 38 TeV HBLs that have been studied with very long baseline interferometry at multiple epochs. The highest 2{sigma} apparent speed lower limit considering all sources is 3.6c. This suggests that bulk Lorentz factors of up to about 4, but probably not much higher, exist in the parsec-scale radio-emitting regions of these sources, consistent with estimates obtained in the radio by other means such as brightness temperatures. This can be reconciled with the high Lorentz factors estimated from the high-energy data if the jet has velocity structures consisting of different emission regions with different Lorentz factors. In particular, we analyze the current apparent speed data for the TeV HBLs in the context of a model with a fast central spine and a slower outer layer.
- ID:
- ivo://CDS.VizieR/J/A+A/495/691
- Title:
- Multifrequency catalogue of blazars, Roma-BZCAT
- Short Name:
- J/A+A/495/691
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalogue of blazars based on multifrequency surveys and on an extensive review of the literature. Blazars are classified as BL Lacertae objects, as flat spectrum radio quasars or as blazars of uncertain/transitional type. Each object is identified by a root name, coded as BZB, BZQ and BZU for these three subclasses respectively, and by its coordinates. This catalogue is being built as a tool useful for the identification of the extragalactic sources that will be detected by present and future experiments for X and gamma-ray astronomy, like Swift, AGILE, Fermi-GLAST and Simbol-X. An electronic version is available from the ASI Science Data Center web site at http://www.asdc.asi.it/bzcat.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/97
- Title:
- Multiple lensed images in MCS J1206.2-0847
- Short Name:
- J/ApJ/749/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847 (z=0.44) using UV, Optical, and IR, HST/ACS/WFC3 data taken as part of the CLASH multi-cycle treasury program, with VLT/VIMOS spectroscopy for some of the multiply lensed arcs. The CLASH observations, combined with our mass model, allow us to identify 47 new multiply lensed images of 12 distant sources. These images, along with the previously known arc, span the redshift range 1<~z<~5.5, and thus enable us to derive a detailed mass distribution and to accurately constrain, for the first time, the inner mass profile of this cluster. We find an inner profile slope of dlog{Sigma}/dlog{theta}=~-0.55+/-0.1 (in the range [1",53"], or 5kpc<~r<~300kpc), as commonly found for relaxed and well-concentrated clusters. Using the many systems uncovered here we derive credible critical curves and Einstein radii for different source redshifts. For a source at z_s_=~2.5, the critical curve encloses a large area with an effective Einstein radius of {theta}_E_=28"+/-3", and a projected mass of (1.34+/-0.15)x10^14^M_{sun}_. From the current understanding of structure formation in concordance cosmology, these values are relatively high for clusters at z~0.5, so that detailed studies of the inner mass distribution of clusters such as MACS J1206.2-0847 can provide stringent tests of the {Lambda}CDM paradigm.